I use a batch file to copy in %temp% mpam-fe.exe and to execute it. When executed from scheduled task on Windows 2008R2 i can't update. In the %temp% directory is genereated MpSigStub.log with this content:
Command: MpSigStub.exe /program C:\Users\ingres\AppData\Local\Temp\mpam-fe.exe
Start time: 14/08/2015 23:46 (version 11.1.5128.0)
=================================== ProductSearch ==================================
ERROR 0x8007000e : CreateAntimalwareProduct(FCS v1)
ERROR 0x80070645 : No installed products found
ERROR 0x80070645 : SearchForInstalledProducts
ERROR 0x80070645 : MpSigStubMain
End time: 14/08/2015 23:46
Signatures are perfectly updated when batch is executed directly.
I've a similar scheduled task on 2003 R2 Server and it works well.
Thanks.